1. Field of the Invention
The present invention relates to a motor control device and a motor control method.
2. Description of the Related Art
In the prior art, control devices have been known which includes: a first estimation device which includes current sensors for detecting the current for each of the phases of, for example, a three-phase AC motor, and which estimates the current value of any one phase among the three phases from detection values of the current sensors for the other two phases; a second estimation device, for estimating the current value of any one phase among the three phases from the phase angle of current supplied to the three-phase AC motor and from detection values of current sensors for the other two phases; and a malfunction detection portion which, based on detection values of current sensors and on current values estimated by the first and second estimation devices, judges whether there is a malfunction in the current sensors for each phase, and upon judging that the current sensor for any phase among the three phases is malfunctioning, uses the current value estimated for the phase corresponding to the malfunctioning current sensor in calculations of motor control currents (see, for example, Japanese Unexamined Patent Application, First Publication No. 2000-116176).
In this control device, the outputs of current sensors for each phase are input to the malfunction detection portion, and current estimation values are estimated in the malfunction detection portion based on detection values for current sensors; in addition, malfunctions of current sensors are judged based on each of these current estimation values, and motor control currents are output in response to this judgment result.
However, when as a result of comparison of current values based on the detection values of a plurality of current sensors, as in the above-described control device of the prior art, that is, when malfunctioning of current sensors for each phase is judged according to the result of judgments as to whether detection values of a plurality of current values and the current estimation values based on detection values of a plurality of current sensors are the same, it is assumed that the detection value of each current sensor is the value for an equivalent phase angle. For this reason, the precision of detection timing of each of the current sensors makes a relatively large contribution to malfunction judgments for each current sensor, and so there may be difficulty in continuing output of appropriate motor control currents.
The present invention was made in view of the above circumstances, and has an object of providing a motor control device and a motor control method enabling continuation of appropriate control of a three-phase AC motor.